Bearing device for crankshaft of internal combustion engine

ABSTRACT

The invention provides a bearing device, including a crankshaft, a pair of half bearings each having crush reliefs adjacent to both circumferential ends thereof, a bearing housing having a retaining hole, and one half thrust bearing arranged adjacent to the retaining hole. Each half thrust bearing is configured at least by a bearing alloy layer and a resin slide layer which constitutes a slide surface receiving an axial force of the crankshaft, and thrust reliefs adjacent to both circumferential end portions of the sliding surface so that its wall thickness is made thinner toward the circumferential end surface. A thrust relief length at an inner end portion of the thrust relief positioned on a rear side in the crankshaft rotational direction is formed to be larger than a thrust relief length at an inner end portion of the thrust relief positioned on a front side.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromJapanese Patent Application No. 2015-166564 filed on Aug. 26, 2015. Theentire disclosure of the above application is incorporated herein byreference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a bearing device that receives an axialforce of a crankshaft of an internal combustion engine.

(2) Description of Related Art

A crankshaft of an internal combustion engine is rotatably supported, atits journal portion, by a lower part of a cylinder block of an internalcombustion engine via a main bearing which is configured by assembling apair of half bearings into a cylindrical shape.

One or both of the pair of half bearings is used to be combined with ahalf thrust bearing which receives an axial force of the crankshaft. Thehalf thrust bearing is provided at one or both of axial end surfaces ofthe half bearing.

The half thrust bearing receives the axial force generated in thecrankshaft. That is, the half thrust bearing is placed for the purposeof bearing the axial force applied to the crankshaft when the crankshaftis connected to a transmission via a clutch, for example.

On a sliding surface side of the half thrust bearing close to bothcircumferential ends thereof, thrust reliefs are formed so that abearing member becomes thinner toward the respective circumferential endsurfaces. In general, the thrust relief is formed so that a length fromthe circumferential end surface to the sliding surface of the halfthrust bearing, and a depth at the circumferential end surface areconstant irrespective of the position in a radial direction. The thrustrelief is formed in order to absorb misalignment of the end surfaces ofthe pair of half thrust bearings when mounting the half thrust bearingson a split type bearing housing (see FIG. 10 of JP-A-11-201145).

The crankshaft of the internal combustion engine is supported, at itsjournal portion, by the lower part of the cylinder block of the internalcombustion engine via the main bearing consisting of the pair of halfbearings. Here, lubrication oil is fed from an oil gallery in a wall ofthe cylinder block through a through hole in a wall of the main bearinginto a lubrication oil groove formed along an inner circumferentialsurface of the main bearing. The lubrication oil is supplied to thelubrication oil groove of the main bearing in this manner, and thensupplied to the half thrust bearings.

In general, a laminated structure in which an aluminium bearing alloylayer or a cupper bearing alloy layer is formed on one surface of asteel back metal is used for a thrust bearing which receives an axialforce of a crankshaft of an internal combustion engine. Further, thereis proposed a thrust bearing improved in conformability, fatigueresistance or load carrying capacity by applying a resin slide layer onthe aluminium bearing alloy layer or the cupper bearing alloy layer (seeJP-A-H07-238936). As a material used for the resin slide layer, there isa material in which a solid lubricant is added to a resin obtained bypolymer-alloying a heat-resistant resin such as polyamide imide havinghigh strength and excellent heat resistance with polyamide or the like(see JP-A-2008-308595).

Meanwhile, in recent years, oil pumps for supplying lubrication oil ofinternal combustion engines have been reduced in size, so that theamount of lubrication oil to be supplied to the bearings decreases.Accordingly, the amount of lubrication oil leaking through the endsurfaces of the main bearing tends to decrease, and the amount oflubrication oil supplied to the half thrust bearings also tends todecrease. To address this, there is proposed an art for improvingretainability of lubrication oil by forming a plurality of narrowgrooves in parallel on the sliding surfaces of the half thrust bearings,for example (see JP-A-2001-323928).

BRIEF SUMMARY OF THE INVENTION

Further, in recent years, crankshafts have been reduced in diameter forreducing the weight of internal combustion engines, so that the rigidityof the crankshafts becomes low. Accordingly, the crankshaft tends todeform easily during operation of the internal combustion engine, andthe vibration of the crankshaft tends to become large. As a result, thesliding surface near a circumferentially central portion of the halfthrust bearing tends to directly contact with a thrust collar surface ofthe crankshaft, so that damage easily occurs on a surface of a resinslide layer constituting the slide surface of the half thrust bearing.

JP-A-2001-323928 discloses a configuration in which the oil grooves areprovided on the sliding surface to supply the lubrication oil to almostthe entire bearing surface. However, even if adopting the art ofJP-A-2001-323928, it is difficult to prevent the sliding surface,particularly adjacent to the thrust relief on a rear side of the halfthrust bearing in a crankshaft rotational direction from contacting withthe thrust collar of the crankshaft if the vibration of the crankshaftdue to the deformation is large as above. Therefore, there has been apossibility that damage occurs in the sliding surface of the half thrustbearing.

Accordingly, an object of the present invention is to provide a bearingdevice for a crankshaft of an internal combustion engine, in which thedamage hardly occurs during operation of the internal combustion engine.

According to the present invention, there is provided a bearing device(1) for a crankshaft of an internal combustion engine, including:

a crankshaft;

a pair of half bearings (7, 7) for supporting a journal portion of thecrankshaft, crush reliefs (73, 73) being formed on an innercircumferential surface of each half bearing and adjacent to bothcircumferential ends of the half bearing;

a bearing housing (4) having a retaining hole (5) for retaining the pairof half bearings, the retaining hole being formed to penetrate throughthe bearing housing; and

one half thrust bearing (8) having a semi-annular shape that is arrangedadjacent to the retaining hole on each axial end surface of the bearinghousing, each half thrust bearing (8) being configured by a bearingalloy layer (16) and a resin slide layer (18), or by a back metal layer(14), a bearing alloy layer (16) and a resin slide layer (18), the resinslide layer (18) constituting a slide surface (81) which receives anaxial force of the crankshaft, wherein at least one of the half thrustbearings includes thrust reliefs (82F, 82R) on a front side and a rearside in a crankshaft rotational direction, the thrust reliefs beingarranged adjacent to both circumferential end portions of a slidingsurface (81) receiving an axial force of the crankshaft, and beingformed so that a wall thickness of the half thrust bearing is madethinner toward the circumferential end surfaces of the thrust bearing,and

a length (L2) at a radially inner end portion of the thrust relief (82R)positioned on the rear side of the half thrust bearing in the crankshaftrotational direction is larger than a length (L1) at a radially innerend portion of the thrust relief (82F) positioned on the front side inthe crankshaft rotational direction.

Here, the crankshaft is a member including a journal portion, a crankpinportion, and a crank arm portion. While the half thrust bearing is amember having a shape obtained by dividing an annular shape intoapproximately halves, it is not intended to be strictly half.

The bearing device for a crankshaft of the present invention receives anaxial force of a crankshaft of an internal combustion engine. A thrustrelief length at an inner end portion of a thrust relief positioned on arear side in a crankshaft rotational direction is formed so as to belonger than a thrust relief length at an inner end portion of a thrustrelief positioned on a front side in the crankshaft rotationaldirection. By this configuration, lubrication oil flowing out of crushreliefs of a pair of half bearings easily flows into a thrust reliefclearance formed by the thrust relief positioned on the rear side in thecrankshaft rotational direction, and hardly flows into a thrust reliefclearance formed by the thrust relief positioned on the front side inthe crankshaft rotational direction, so that a large amount of thelubrication oil is fed to the sliding surface of the thrust bearing.Accordingly, even when the deformation of the crankshaft is generatedduring the operation of the internal combustion engine and therefore thevibration becomes large, a sliding surface of the thrust bearing hardlycomes into direct contact with a thrust collar surface of thecrankshaft, so that damage of a surface on the resin slide layerconstituting the sliding surface of the half thrust bearing hardlyoccurs. Further, according to this configuration, a load capability ishigh since the area of the sliding surface of the thrust bearing is notreduced.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exploded perspective view of a bearing device;

FIG. 2 is a cross-sectional view of a half thrust bearing of embodiment1;

FIG. 3 is a front view of the half thrust bearing of embodiment 1;

FIG. 4A is a side view of a thrust relief of the half thrust bearing inFIG. 3 seen in the direction of arrow Y1;

FIG. 4B is a side view of a thrust relief of the half thrust bearing inFIG. 3 seen in the direction of arrow Y2;

FIG. 5 is a front view of a bearing device;

FIG. 6 is a cross-sectional view of the bearing device;

FIG. 7 is a front view of a half thrust bearing of embodiment 2;

FIG. 8 is a front view of a half thrust bearing of embodiment 3;

FIG. 9 is an end view of a half thrust bearing in FIG. 8 seen in thedirection of arrow Y3, illustrating a circumferential end surface of athrust relief positioned on a rear side in a crankshaft rotationaldirection;

FIG. 10 is an end view of a half thrust bearing in FIG. 8 seen in thedirection of arrow Y4, illustrating a circumferential end surface of athrust relief positioned on a front side in the crankshaft rotationaldirection;

FIG. 11 is a front view of a half thrust bearing of embodiment 4;

FIG. 12 is a side view showing a circumferential end surface of a thrustrelief positioned on a rear side of the half thrust bearing in FIG. 11in the crankshaft rotational direction seen in the direction of arrowY5;

FIG. 13 is a side view showing a circumferential end surface of a thrustrelief positioned on a front side of the half thrust bearing in FIG. 11in the crankshaft rotational direction, seen in the direction of arrowY6;

FIG. 14 is a side view of a thrust relief positioned on a rear side of ahalf thrust bearing in the crankshaft rotational direction of anotherembodiment;

FIG. 15 is a front view of a half thrust bearing of another embodiment;

FIG. 16 is a front view of a thrust bearing of another embodiment;

FIG. 17A is a front view of half bearings and a half thrust bearing forexplaining operation of the embodiment;

FIG. 17B is a view showing an inner side of the half bearings and thehalf thrust bearing in FIG. 17A as seen from the inside in a radialdirection;

FIG. 18 is a front view of a half bearing; and

FIG. 19 is a bottom view of the half bearing in FIG. 18, seen from theinside in a radial direction.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

Embodiment 1

(General Configuration of Bearing Device)

First, a description will be given for a general configuration of abearing device 1 having a half thrust bearing 8 of the presentinvention, using FIGS. 1, 5, and 6. As shown in FIGS. 1, 5, and 6, abearing housing 4 configured by attaching a bearing cap 3 to a lowerpart of a cylinder block 2 has a bearing hole 5 which is a circular holepenetrating between side surfaces of the cylinder block 2 and thebearing cap 3. The side surfaces of the cylinder block 2 have seats 6,which are semi-annular recesses, on the periphery of the bearing hole 5.Half bearings 7 and 7 are assembled in a cylindrical shape and fittedinto the bearing hole 5. The half bearings 7 and 7 rotatably support ajournal portion 11 of a crankshaft which rotates in one direction. Ahalf thrust bearing 8 is fitted into the seat 6. The half thrust bearing8 receives an axial force f (see FIG. 6) via a thrust collar 12 of thecrankshaft. An axial length of the bearing cap 3 is larger than an axiallength of the cylinder block 2 at a position of the seat 5, so that bothcircumferential end surfaces of the half thrust bearing 8 are adapted tobe in contact with a split surface of the bearing cap 3.

As shown in FIG. 5, a lubrication oil groove 71 is formed on an innercircumferential surface of the half bearing 7 (the upper one) on a sideof the cylinder block 2 of the half bearings 7 constituting a mainbearing, and a through hole 72 is formed to penetrate the half bearing 7from the lubrication oil groove 71 to an outer circumferential surface(also see FIGS. 18 and 19). It is to be noted that the lubrication oilgroove may be formed on both of the upper and lower half bearings.

Further, each half bearing 7 has crush reliefs 73 and 73 on both endsthereof adjacent to abutment surfaces of the half bearings 7 (see FIG.5). The crush reliefs 73 are wall-thickness reduction regions formed sothat a wall thickness of a region adjacent to circumferential endsurfaces of the half bearing 7 is gradually reduced toward thecircumferential end surface. The crush reliefs 73 are formed forabsorbing misalignment and deformation of abutment surfaces whenassembling the pair of half bearings 7 and 7.

(Configuration of Half Thrust Bearing)

Next, the configuration of the half thrust bearing 8 of embodiment 1will be described with reference to FIGS. 2 to 6. The half thrustbearing 8 is formed by, first, forming a semi-annular shaped flat platefrom a bimetal obtained by bonding a thin bearing alloy layer 16 to asteel back metal layer 14, and then forming a resin slide layer 18 onthe bearing alloy layer 16. The half thrust bearing 8 includes a slidingsurface 81 (bearing surface) at a central region that is a surfaceconfigured by the resin slide layer 18, and thrust reliefs 82R and 82Fat regions adjacent to end surfaces 83 and 83 on both circumferentialsides of the half thrust bearing 8. In order to improve retainability ofthe lubrication oil, two oil grooves 81 a and 81 a are formed betweenthe opposite thrust reliefs 82R and 82F on the sliding surface 81.

The resin slide layer 18 is formed of a resin binder and a solidlubricant. While known resins may be used as a resin binder, it ispreferable to use one or more of polyamide imide, polyimide andpolybenzimidazole with high heat-resistance. Further, the resin bindermay be a resin composition obtained by mixing a high heat-resistantresin consisting of one or more of polyamide imide, polyimide andpolybenzimidazole and a resin of 1 to 25 vol. % consisting of one ormore of polyamide, epoxy and polyether sulfone, or a resin compositionobtained by polymer-alloying them. As a solid lubricant, it is possibleto use molybdenum disulfide, tungsten disulfide, graphite,polytetrafluorethylene, boron nitride or the like. The ratio of additionof the solid lubricant to the resin slide layer is preferably 20 to 80vol. %. In order to improve wear resistance of the resin slide layer,hard particles made of a ceramic material, an intermetallic compound orthe like may be contained in the ratio of 0.1 to 10 vol. % to the resinslide layer.

For forming the resin slide layer 18 on a slide surface side of the halfthrust bearing 8, a composition of the resin slide layer diluted with anorganic solvent is applied onto the bearing alloy layer 16 of the halfthrust bearing by a spray method, the organic solvent is dried byheating, and then the resin composition is baked by heating. However,the forming method of the resin slide layer 18 is not limited to thespray method, and the resin slide layer 18 may be formed by anothercommon method such as a roll coat method, a print method or the like.

It will be understood that a resin slide material having the samecomposition as the resin slide layer may be applied not only onto theslide surface 81 receiving the axial force of the crankshaft but alsoonto a surface of the thrust relief 82, a surface of the oil groove 81a, an outer radial surface of the half thrust bearing, an inner radialsurface thereof, and the like. For example, in embodiments 1 to 4described below, the resin slide material is applied also onto thesurfaces of the thrust reliefs 82, 82 of the half thrust bearing 8, andthe surfaces of the oil grooves 81 a, 81 a.

The thickness of the resin slide layer 18 is 1 to 30 μm, preferably 2 to20 μm, and more preferably 3 to 8 μm.

As shown in FIGS. 4A and 4B, the thrust reliefs 82R and 82F arewall-thickness reduction regions formed adjacent to end surfaces of thesliding surface 81 on both circumferential sides so that the wallthickness is gradually reduced toward the end surface of the half thrustbearing 8. The thrust reliefs 82R and 82F are formed over the entireradial length of the circumferential end surfaces 83 of the half thrustbearing 8. The thrust reliefs 82R and 82F are formed to alleviatemisalignment between the circumferential end surface 83 of the thrustbearing 8 and an end surface of the bearing cap that are to be incontact with each other, that may be caused by misalignment and the likebetween end surfaces of the respective split type bearing housings 2 and3 when mounting the half thrust bearing 8 on the split type bearinghousing 4.

The surfaces of the thrust reliefs 82R and 82F are configured by flatsurfaces in embodiment 1, but may be configured by curved surfaces (FIG.13). In the case of flat surfaces, the surfaces may be configured by asingle flat surface, or by combining a plurality of flat surfaces. Alsoin the case of curved surfaces, the surface may be configured by asingle curved surface, or by combining a plurality of curved surfaces.Further, the surface of each thrust reliefs 82R and 82F may beconfigured by combining a flat surface and a curved surface (FIG. 12).

As will be understood from FIGS. 3 and 5, when the half thrust bearing 8of the embodiment is mounted on the bearing housing 4 of the bearingdevice 1, a thrust relief length L2 at an inner end portion of thethrust relief 82R on a side of the circumferential end surface 83 whichis assembled so as to be positioned on a rear side in the rotationaldirection of the crankshaft rotating in one direction (hereinafter,referred to as “rear side thrust relief”) is formed to differ from, andlonger than a thrust relief length L1 at an inner end portion of thethrust relief 82F on a side of the circumferential end surface 83positioned on a front side in the crankshaft rotational direction(hereinafter, referred to as “front side thrust relief”). Here, inembodiment 1, the thrust relief length of the rear side thrust relief82R and the thrust relief length of the front side thrust relief 82F areformed to be constant between the inner end portion and an outer endportion.

Here, the “thrust relief length” means a length measured vertically froma plane (imaginary dividing plane H) passing through both end surfaces83 and 83 of the one half thrust bearing 8 to the other end of thethrust relief (FIG. 3). More specifically, the thrust relief lengths L1and L2 at the inner end portion are respectively defined as lengths fromthe imaginary dividing plane H to the points where the surfaces of thethrust reliefs 82F and 82R intersect the inner circumferential edge ofthe sliding surface 81.

Further, the “thrust relief positioned on a rear side in the crankshaftrotational direction” means the thrust relief 82R of the thrust reliefsat both circumferential end portions of one half thrust bearing 8, thatfirstly passes through any point on the thrust collar 12 of the rotatingcrankshaft, and the “thrust relief positioned on a front side in thecrankshaft rotational direction” means the thrust relief 82F whichsecondly passes through the point.

FIG. 4A shows a side near the circumferential end surface 83 on the rearside of the half thrust bearing 8 in the crankshaft rotational directionseen from the inner side (in the direction of arrow Y1 in FIG. 3). FIG.4B shows a side near the other circumferential end surface 83 on thefront side of the thrust bearing 8 in the crankshaft rotationaldirection seen from the inner side (in the direction of arrow Y2 in FIG.3).

As shown in FIGS. 4A and 4B, the portion of the sliding surface 81 has athickness t. The surfaces of the front side thrust relief 82F and therear side thrust relief 82R of the half thrust bearing 8 have the samethrust relief depth RD at the circumferential end surfaces. Inembodiment 1, the thrust relief depth RD of the front side thrust relief82F and the rear side thrust relief 82R at the circumferential endsurfaces is constant also between the inner end portion and the outerend portion in the radial direction.

Here, the “thrust relief depth” means an axial distance from a planecontaining the sliding surface 81 of the half thrust bearing 8 to thesurface of the thrust relief. In other words, the thrust relief depth isa distance measured vertically from an imaginary sliding surfaceobtained by extending the sliding surface 81 over the thrust reliefs 82Fand 82R. Hence, the thrust relief depth RD at the circumferential endsurface is defined as an axial distance from the surface of the thrustrelief at the circumferential end surface of the half thrust bearing 8to the imaginary sliding surface.

As specific dimensions of the front side thrust relief 82F and the rearside thrust relief 82R, the thrust relief depth RD at thecircumferential end surface of the half thrust bearing 8 from thesliding surface 81 to the front side thrust relief 82F and the rear sidethrust relief 82R may be 0.3 mm to 1.0 mm, for example, when the thrustbearing is used for a crankshaft of a small internal combustion enginefor a passenger car and the like (in which a journal portion diameter isabout 30 to 100 mm). It is to be noted that the front side thrust relief82F and the rear side thrust relief 82R have the same thrust reliefdepth RD. The thrust relief length L1 of the front side thrust relief82F at the inner end portion may be 1 mm to 5 mm, and the thrust relieflength L2 of the rear side thrust relief 82R at the inner end portionmay be 5 mm to 25 mm. It is to be noted that the above dimensions aremerely examples, and the dimensions are not limited to these ranges.

The foregoing numerical ranges of the thrust relief length L1 of thefront side thrust relief 82F and the thrust relief length L2 of the rearside thrust relief 82R are partially overlapped with each other.However, this is because the larger the bearing is, the longer thethrust relief length needs to be. Accordingly, the thrust relief lengthsL1 and L2 should satisfy the relation L2>L1 within their respectivenumerical ranges.

As shown in FIG. 8, the rear side thrust relief is preferably formedwithin a range of a circumferential angle θ1 of 25° or less from thecircumferential end surface 83 of the half thrust bearing 8, and thefront side thrust relief is preferably formed within a range of acircumferential angle θ2 of 5° or less from the circumferential endsurface 83 of the half thrust bearing 8.

(Operation)

Next, the operation of the bearing device 1 of the embodiment will bedescribed, using FIGS. 5, 6, 17A, and 17B.

(Oil Supply Operation)

In the bearing device 1, the lubrication oil discharged by pressurizedfrom an oil pump (not shown) passes an internal oil passage of thecylinder block 2 and the through hole 72 penetrating the wall of thehalf bearing 7, and is supplied to the lubrication oil groove 71 on theinner circumferential surface of the half bearing 7. The lubrication oilsupplied into the lubrication oil groove 71 is partly supplied to theinner circumferential surface of the half bearing 7, partly fed throughan opening (not shown) for an internal oil passage of the crankshaftprovided on a surface of the journal portion toward a crankpin, andfurther, partly passes through a clearance between the surface of thecrush reliefs 73 of the pair of half bearings 7 and 7 forming the mainbearing and the surface of the journal portion 11 of the crankshaft toflow from both axial ends of the half bearings 7 and 7 to the outside.

In the embodiment, the half bearings 7 are arranged concentrically withthe half thrust bearing 8, and a plane containing both circumferentialend surfaces of the half bearings 7 constituting the main bearing ismade parallel to a plane containing both circumferential end surfaces ofthe half thrust bearing 8, so that the positions of the crush reliefs 73correspond to those of the thrust reliefs 82F and 82R.

In addition to the relation between the thrust relief length L1 and thethrust relief length L2, the half thrust bearing 8 of the embodiment hasthe following relation to the half bearing 7.

That is to say, in the half thrust bearing 8 of the embodiment, thethrust relief length L2 of the rear side thrust relief 82R at the innerend portion is longer than the crush relief length CL of the crushrelief 73 of the corresponding half bearing 7.

In addition, in the half thrust bearing 8 of the embodiment, the thrustrelief length L1 of the front side thrust relief 82F at the inner endportion is shorter than the crush relief length CL (FIG. 18) of thecrush relief 73 of the corresponding half bearing 7.

Here, the “crush relief length CL” of the crush relief 73 means a lengthof the crush relief 73 disposed correspondingly to the position of therear side thrust relief 82R or the position of the front side thrustrelief 82F at the axial end portion on the side where the half thrustbearing 8 is provided (FIG. 5). In particular, the crush relief lengthCL is expressed by, when the half bearing 7 is placed on a horizontalsurface such that both circumferential end surfaces 74 and 74 become alower end surface, a height from the horizontal surface to an upper edgeof the crush relief 73 (FIG. 18). It is to be noted that the crushreliefs 73 at both circumferential end portions of the half bearing 7have the same crush relief length. Alternatively, unlike the embodiment,the crush relief length of the crush reliefs 73 of the half bearing 7may be varied in the axil direction of the half bearing 7.

As specific dimensions of the crush relief 73 of the half bearing 7, adepth of the crush relief 73 at the end surface 74 measured from animaginary extended surface obtained by extending the sliding surface 75over the crush relief is 0.01 to 0.1 mm, and the crush relief length CLis 3 to 7 mm when used for a crankshaft (in which a journal portiondiameter is about 30 to 100 mm) of a small internal combustion enginefor a passenger car, for example.

Also, the thrust relief length L2 of the rear side thrust relief 82R ofthe half thrust bearing 8 at the inner end portion preferably satisfiesthe formula: L2≧1.5×CL with respect to the crush relief length CL of thecrush relief of the correspondingly positioned half bearing 7. Further,the thrust relief length L1 of the front side thrust relief 82F of thehalf thrust bearing 8 at the inner end portion preferably satisfies theformula: L1≦1.5×CL with respect to the crush relief length CL of thecrush relief 73 of the correspondingly positioned half bearing 7.

Hereinafter, the operation of the present invention will be described.

Immediately after flowing out of the clearance between the crush reliefsof the half bearings 7, the lubrication oil flows toward a front side inthe crankshaft rotational direction from the position of acircumferential end surface 83 of the half thrust bearing 8 as shown inFIGS. 17A and 17B (dashed arrow) due to an inertial force causing theoil to move on the front side in the rotational direction of thecrankshaft 11 because the lubrication oil has circumferentially flownwith the surface of the journal portion of the rotating crankshaft.

In the half thrust bearing 8 of the embodiment, the thrust relief lengthL2 at the radial inner end portion of the rear side thrust relief 82R islonger than the thrust relief length L1 at the radial inner end portionof the front side thrust relief 82F. According to the configuration, thelubrication oil flown out of the crush relief clearance of the halfbearings 7 and then flowing toward the front side in the rotationaldirection of the crankshaft 11 relative to the position of thecircumferential end surface 83 of the half thrust bearing 8 flows intothe thrust relief clearance S at the inner end portion of the halfthrust bearing 8 in large amounts, and is then fed to the slidingsurface 81. Here, the “thrust relief clearance S” means a clearancesurrounded by the surface of the rear side thrust relief 82R of the halfthrust bearing 8, an imaginary surface obtained by extending the slidingsurface 81 over the surface of the rear side thrust relief 82R, and aplane containing the circumferential end surfaces of the half thrustbearing 8 (see FIG. 17B).

More specifically, the lubrication oil in the crush relief clearance ofthe half bearing 7 is fed toward the front side in the journalrotational direction with the surface of the journal. However, since thevolume of the crush relief clearance becomes smaller toward the frontside in the journal rotational direction, the amount of the lubricationoil flowing out of the crush relief clearance to the outside becomeslarge at this small volume region. Here, if the crush relief length isshorter than the thrust relief length on the rear side, the lubricationoil flowing out of the small volume region flows into the thrust reliefclearance of the rear side thrust relief 82R more easily (see FIGS. 17Aand 17B).

The lubrication oil flowing out of the crush relief clearances of thehalf bearings 7 and flowing forward the front side in the rotationaldirection of the crankshaft 11 beyond the position of thecircumferential end surface 83 of the half thrust bearing 8 partly flowsinto a clearance formed by the inner circumferential surface of the halfthrust bearing 8, the surface of the journal portion 11 of thecrankshaft, the thrust collar surface 12 of the crankshaft, and an axialend surface of the half bearing (see FIGS. 17A and 17B). The lubricationoil flowing into the clearance is fed forward the front side in thecrankshaft rotational direction with the thrust collar surface of therotating crankshaft, then flows into the thrust relief clearance of thefront side thrust relief 82F of the half thrust bearing 8, and isdischarged to the outside.

In the half thrust bearing 8 of the embodiment, a thrust reliefclearance S of the front side thrust relief 82F at the inner end portionof the half thrust bearing 8 (that is, a clearance surrounded by thesurface of the front side thrust relief 82F of the half thrust bearing8, the imaginary surface obtained by extending the sliding surface 81over the surface of the front side thrust relief 82F, and the planecontaining the circumferential end surfaces of the half thrust bearing8) is smaller than the thrust relief clearance S of the rear side thrustrelief 82R. Accordingly, the lubrication oil is inhibited from flowinginto the thrust relief clearance of the front side thrust relief 82F,and thus is hardly discharged to the outside. Therefore, the clearanceformed by the inner circumferential surface of the half thrust bearing,the surface of the journal portion 11 of the crankshaft, the thrustcollar surface 12 of the crankshaft, and the axial end surface of thehalf bearing 7 tends to be filled with the lubrication oil, while thelubrication oil also flows to the sliding surface under the effect ofcentrifugal force during the lubrication oil is transferred toward thefront side in the circumferential direction with the thrust collarsurface 12 of the rotating crankshaft. As a result, in the half thrustbearing 8 of the embodiment, the lubrication oil is easily supplied tothe sliding surface 81 not only in an area close to the thrust relief82R on the rear side, but also in the entire area.

Further, by the configuration in which the crush relief length of thehalf bearing 7 is longer than the thrust relief length on the frontside, the lubrication oil flowing out of the crush relief clearance (theclearance formed by the crush relief on the front side of the halfbearing 7 in the shaft rotational direction which crush relief is in aposition corresponding to the front side thrust relief 82F of the halfthrust bearing 8) is inhibited from flowing through the thrust reliefclearance of the front side thrust relief 82F to the outside.Accordingly, at the area close to the circumferential end surface 83 onthe front side in the crankshaft rotational direction of the half thrustbearing 8, the clearance formed by the inner circumferential surface ofthe half thrust bearing, the surface of the journal portion 11 of thecrankshaft, the thrust collar surface 12 of the crankshaft, and theaxial end surface of the half bearing is easily filled with thelubrication oil.

During the operation of the internal combustion engine, the deformationof the crankshaft (deflection in the axial direction) occurs especiallyunder the operation condition in which the crankshaft is rotated at highspeeds, and thereby the vibration of the crankshaft becomes large. Thelarge vibration periodically causes an axial force f in the crankshafttoward the sliding surface 81 of the half thrust bearing 8. The slidingsurface 81 of the half thrust bearing 8 receives the axial force f.

In the bearing device 1 of the present invention, even if the axialforce f of the crankshaft acts on the half thrust bearing 8, thelubrication oil flown out of the crush relief clearance between the pairof half bearings 7 easily flows into the thrust relief clearance S inlarge amounts that is formed by the rear side thrust relief 82R of thehalf thrust bearing 8, and hardly flows into the thrust relief clearanceformed by the front side thrust relief 82F of the half thrust bearing 8,so that a large amount of lubrication oil is fed to the sliding surface81 as described above. Since the large amount of lubrication oil issupplied, the sliding surface 81 of the half thrust bearing 8 hardlycomes into direct contact with the surface of the thrust collar 12 ofthe crankshaft.

In the half thrust bearing 8 of the embodiment, the thrust relief lengthL2 of the thrust relief 82R on the rear side is longer than the thrustrelief length L1 of the front side thrust relief 82F. With respect tothe ability of receiving a load, the configuration of the embodimentwill be described as compared to a configuration of a conventionalthrust bearing in which thrust reliefs with the same length are formedin both circumferential end portions thereof. In the thrust bearing ofthe conventional half thrust bearing having the thrust reliefs with thesame length, if the lengths of the thrust reliefs on bothcircumferential sides are increased for increasing the amount oflubrication oil flowing into the thrust relief clearance after flowingout of the crush relief clearance of the main bearing (half bearings),the area of the sliding surface of the half thrust bearing is reduced,and thus the ability of the half thrust bearing of receiving the axialload of the crankshaft is decreased. In contrast, in the configurationof the embodiment, the thrust relief length L2 of the thrust relief 82Ron the rear side is longer than the thrust relief length L1 of the frontside thrust relief 82F, in other words, the sliding surface of theconventional half thrust bearing is shifted on the front side in thecrankshaft rotational direction, and thus, the configuration of theembodiment does not involve the reduction of the area of the slidingsurface 81. As a result, the ability of receiving (bearing) the axialload of the crankshaft is still high in the half thrust bearing 8 of thebearing device 1 of the present invention.

Embodiment 2

Hereinafter, a description will be given, using FIG. 7, for a halfthrust bearing 8A having a front side thrust relief 82F and a rear sidethrust relief 82R which are another than those in embodiment 1. Theparts identical or equal to those in embodiment 1 will be described withthe same reference characters.

(Configuration)

The configuration will be described first. The configuration of the halfthrust bearing 8A according to the embodiment is generally similar tothat in embodiment 1 except for the shapes of the front side thrustrelief 82F and the rear side thrust relief 82R.

More specifically, a surface of the rear side thrust relief 82R of thehalf thrust bearing 8A of the embodiment is constituted by a flatsurface, and as shown in FIG. 7, a thrust relief length L2 is configuredso as to be minimum (L2I) at the radially inner end portion and maximum(L2O) at the radially outer end portion. A surface of the front sidethrust relief 82F is also constituted by a flat surface, and as shown inFIG. 7, a thrust relief length L1 is configured so as to be maximum(L1I) at the radially inner end portion and minimum (L1O) at theradially outer end portion.

On the other hand, other relations such as the relation between thethrust relief lengths L1I and L2I at the inner end portion and therelation between the thrust relief depths RD of the front side thrustrelief and the rear side thrust relief are similar to those inembodiment 1.

The other configurations of embodiment 2 are generally similar to thosein embodiment 1 and therefore, embodiment 2 has operations and effectssimilar to those in embodiment 1.

Embodiment 3

Hereinafter, a description will be given, using FIGS. 8 to 10, for ahalf thrust bearing 8B having a front side thrust relief 82F and a rearside thrust relief 82R which are another than those in embodiments 1 and2. The parts identical or equal to those in embodiments 1 and 2 will bedescribed with the same reference characters.

(Configuration)

The configuration will be described first. The configuration of the halfthrust bearing 8B according to embodiment 3 is generally similar to thatin embodiment 1 except for the shapes of the front side thrust relief82F and the rear side thrust relief 82R.

More specifically, a surface of the rear side thrust relief 82R of eachhalf thrust bearing 8B of the embodiment is constituted by a flatsurface, and as shown in FIG. 8, a thrust relief length L2 is configuredso as to be minimum at the radially inner end portion and maximum at theradially outer end portion. A surface of the front side thrust relief82F is also constituted by a flat surface, and as shown in FIG. 8, asurface of thrust relief length is configured so as to be minimum at theradially inner end portion and maximum at the radially outer endportion.

FIG. 9 shows the circumferential end surface 83 of the half thrustbearing 8B positioned on a rear side in the crankshaft rotationaldirection, seen in the direction of arrow Y3 in FIG. 8, and FIG. 10shows the circumferential end surface 83 of the half thrust bearing 8Bpositioned on a front side in the crankshaft rotational direction, seenin the direction of arrow Y4 in FIG. 8. As shown in FIGS. 9 and 10, inthe half thrust bearing 8B of the embodiment, unlike embodiments 1 and2, the rear side thrust relief 82R and the front side thrust relief 82Fhave the thrust relief depths RD measured from the sliding surface 81that are maximum (RD1) at the inner end portions and minimum (RD2) atthe outer end portions, at the circumferential end surfaces 83 and 83.

As specific dimensions of the thrust reliefs 82R and 82F, the thrustrelief depths RD1 at the inner end portions and the thrust relieflengths L1 and L2 of the thrust reliefs 82R and 82F are similar to thosein embodiment 1, while the thrust relief depths RD2 at the outer endportions may be 0.15 to 0.5 mm when used for a crankshaft (in which ajournal portion diameter is about 30 to 100 mm) of a small internalcombustion engine for a passenger car and the like. The above dimensionsare, however, merely examples, and the dimensions are not limited tothese ranges.

In embodiment 3, the lubrication oil having flown into the thrustreliefs 82R and 82F hardly flows to the outside through the radiallyouter end portions of the thrust reliefs 82R and 82F, and becomes easilysupplied to the sliding surface. The other configurations are generallysimilar to those in embodiment 1 and therefore embodiment 3 hasoperations and effects similar to those in embodiment 1.

Embodiment 4

Hereinafter, a description will be given, using FIGS. 11 to 13, for ahalf thrust bearing 8C having a front side thrust relief 82F and a rearside thrust relief 82R which are another than those in embodiments 1-3.The parts identical or equal to those in embodiments 1-3 will bedescribed with the same reference characters.

(Configuration)

The configuration will be described first. The configuration of the halfthrust bearing 8C according to the embodiment is generally similar tothat in embodiment 1 except for the shapes of the front side thrustrelief 82F and the rear side thrust relief 82R.

FIG. 12 shows a side view of an area near the circumferential endsurface 83 of the half thrust bearing 8C positioned on a rear side inthe crankshaft rotational direction, seen from the inside (in thedirection of arrow Y5 in FIG. 11), and FIG. 13 shows a side view of anarea near the circumferential end surface 83 of the half thrust bearing8C positioned on a front side in the crankshaft rotational direction,seen from the inside (in the direction of arrow Y6 in FIG. 11).

As shown in FIG. 11, in the half thrust bearing 8C of embodiment 4, asurface of the rear side thrust relief 82R is configured by a flatsurface adjacent to the sliding surface 81 and a curved surface(arc-shaped surface) which is adjacent to the circumferential endsurface 83 of the half thrust bearing 8C and is depressed from thesliding surface 81 toward an opposite surface (back face) to be aconcave shape, and a thrust relief length L2 is configured so as to beminimum (L2I) at the inner end portion and becomes longer toward theouter end portion.

A surface of the front side thrust relief 82F is configured by a curvedsurface (arc-shaped surface) depressed from the sliding surface 81toward the opposite surface (back face) to be a concave shape, and athrust relief length L1 is configured so as to be constant between theinner end portion and the outer end portion as shown in FIG. 11. Therelation between the thrust relief length L2 of the rear side thrustrelief 82R and the thrust relief length L1 of the front side thrustrelief 82F at the inner end portions are similar to that in embodiment1.

A thrust relief depth RD of the front side thrust relief 82F at thecircumferential end surface 83 and a thrust relief depth RD of the rearside thrust relief 82R at the circumferential end surface 83 areconstant over the radial entire length of the thrust reliefs.

A length L2′ of the curved surface portion of the rear side thrustrelief 82R shown in FIG. 12 (a length measured vertically from a planecontaining the circumferential end surface 83 of the half thrust bearing8C) is generally the same as a thrust relief length L1 of the front sidethrust relief 82F shown in FIG. 13, and constant between the inner endportion and the outer end portion. The length L2′ of the curved surfaceportion of the rear side thrust relief 82R at the inner end portion maybe 0.5 to 3.5 mm.

The curved surface portion of the rear side thrust relief 82R is formedso that a depth RD′ from the sliding surface 81 to a position where thecurved surface portion is connected to the flat surface portion isconstant over the entire radial length of the thrust relief. The depthRD′ of the curved surface portion of the rear side thrust relief 82Rfrom the sliding surface 81 to a position where the curved surfaceportion is connected to the flat surface portion is preferably 0.005 mmto 0.1 mm.

As shown in FIGS. 12 and 13, the curved surface portion of the rear sidethrust relief 82R and the curved surface of the front side thrust relief82F may be an arc-shaped surface having the same radius of curvature R.However, the curved surface portion of the rear side thrust relief 82Rand the curved surface of the front side thrust relief 82F are notlimited to this, and may be an elliptical arc surface or a free curvedsurface (free-form surface).

The length L2′ of the curved surface portion of the rear side thrustrelief 82R is not limited to the embodiment, and may be configured sothat the length of the curved surface portion becomes longer or shorterfrom the inner end portion toward the outer end portion of the halfthrust bearing.

Also, the flat surface portion of the rear side thrust relief 82R shownin FIG. 12 close to the sliding surface 81 may be changed to a curvedsurface having a radius of curvature R2 and bulging from the back faceside toward the sliding surface 81 side to be a convex shape, as shownin FIG. 14. Although FIG. 14 shows a curved surface having the radius ofcurvature R2, it would be understood that the curved surface portion isnot limited to this and may have an elliptical arc surface or a freecurved surface.

Similarly, the curved surface portion of the rear side thrust relief 82Rshown in FIG. 12 or 14 adjacent to the circumferential end surface 83may be changed to a flat surface. Further, the curved surface portion orthe flat surface portion of the rear side thrust relief 82R adjacent tothe circumferential end surface 83 may be configured so that a depth RD′measured from the sliding surface 81 at the position where the curvedsurface portion or the flat surface portion is connected to the curvedsurface portion or the flat surface portion close to the sliding surface81 becomes deeper or shallower from the inner end portion toward theouter end portion of the half thrust bearing 8C.

The surface of the front side thrust relief 82F is preferably configuredsimilarly to the curved surface portion or the flat surface portion ofthe rear side thrust relief 82R adjacent to the circumferential endsurface 83.

In the embodiment, the description has been given for the bearing device1 using such a type of thrust bearing 10 that the half bearing 7 and thehalf thrust bearing 8 are separated from each other, however, thepresent invention is not limited to this. The present invention alsoencompasses a bearing device 1 using such a type of half thrust bearing8 that the half bearing 7 and the half thrust bearing 8 are integrated.

Embodiments 1-4 of the present invention has been described in detailabove with reference to the drawings, however, the specificconfigurations are not limited to these embodiments, and the presentinvention includes design modifications which do not depart from thegist of the present invention.

For example, as shown in FIG. 15, the present invention may be appliedto a thrust bearing using a half thrust bearing with a protrusionprotruding radially outwardly for positioning and rotation prevention.Also, the circumferential length of the half thrust bearing may beshorter than that of the half thrust bearing 8 shown in embodiment 1,for example, by a predetermined length 51. Also, the half thrust bearing8 may have an arcuate cutout having a radius R on its innercircumferential surface close to the circumferential end surfaces.

When forming the arcuate cutout with the radius R in this manner, thethrust relief lengths L1 and L2 and the thrust relief depths RD of thethrust reliefs 82F and 82R can be expressed by the lengths withreference to extension lines of upper edges of the thrust reliefs 82Fand 82R and the depths with reference to extension surfaces of surfacesof the thrust reliefs 82F and 82R, respectively, that are obtained whenthe arcuate cutout is not formed.

Similarly, the half thrust bearing 8 may have chamfers along thecircumferential direction at the radial outer or inner edge on thesliding surface side. In that case, the thrust relief lengths and thethrust relief depths at the inner end portion and the outer end portioncan be expressed by thrust relief lengths and thrust relief depths atpositions of inner and outer diameter side end portions of the halfthrust bearing, that would exist when the chamfers is not formed.

Further, as emphatically shown in FIG. 16, oil grooves 81 a may beformed on a sliding surface 81 of a half thrust bearing 8D so that eachoil groove 81 has a recessed shape formed by combining the front sidethrust reliefs 82F and the rear side thrust reliefs 82R of the presentinvention. It is to be noted that, although one half thrust bearing hastwo oil grooves 81 a on the sliding surface 81 in the embodiment, thepresent invention is not limited to this, and the half thrust bearingmay have one, or three or more oil grooves. Also, although the oilgrooves 81 a in FIG. 16 are illustrated as having a recessed shapeformed by combining the front side thrust relief 82F and the rear sidethrust relief 82R of the half thrust bearing 8C shown in FIG. 11 as anexample, the shape of the oil grooves 81 a is not limited to this.

Above embodiments have been described for the case where one bearingdevice 1 uses two half thrust bearings 8 of the present invention,however, the present invention is not limited to this. The desiredeffect can also be obtained by using the half thrust bearing 8 of thepresent invention on either of the axial end surfaces of the bearinghousing, and a thrust bearing with thrust reliefs of a conventional orother configuration on the other end surface.

Alternatively, the bearing device 1 of the present invention may adoptthe half thrust bearing 8 of the present invention on either of theaxial end surfaces of the bearing housing, and a half thrust bearinghaving the same shape as that of the half thrust bearing 8 on the otheraxial end surface (in that case, the rear side thrust relief 82R of thehalf thrust bearing of the present invention is positioned on a frontside in the crankshaft rotational direction).

Further, in the embodiments, although the half thrust bearing 8 isdisposed on a side of the cylinder block 2 constituting the bearinghousing 4, the half thrust bearing 8 may be disposed on a side of thebearing cap 3 in the bearing device 1.

Still further, in the above described embodiments, the half thrustbearing consisting of the back metal layer, the bearing alloy layer andthe resin slide layer is described, but the invention is not limitedthereto, and may be replaced with a half thrust bearing consisting of abearing alloy layer and a resin slide layer.

The invention claimed is:
 1. A bearing device for a crankshaft of aninternal combustion engine, comprising: a crankshaft; a pair of halfbearings for supporting a journal portion of the crankshaft, crushreliefs being formed on an inner circumferential surface of each halfbearing and adjacent to both circumferential ends of the half bearing; abearing housing having a retaining hole for retaining the pair of halfbearings, the retaining hole being formed to penetrate through thebearing housing; and two half thrust bearings each having a semi-annularshape that is arranged adjacent to the retaining hole on each axial endsurface of the bearing housing, each half thrust bearing beingconfigured by a bearing alloy layer and a resin slide layer, or by aback metal layer, a bearing alloy layer and a resin slide layer, theresin slide layer constituting a slide surface receiving an axial forceof the crankshaft, wherein at least one of the half thrust bearingscomprises a first thrust relief on a front side and a second thrustrelief on a rear side in a crankshaft rotational direction, the slidingsurface receiving the axial force is arranged between the first andsecond thrust reliefs, and the first and second thrust reliefs beingformed so that a wall thickness of the half thrust bearing is madethinner toward both circumferential ends of the thrust bearing, and athrust relief length at an inner end portion of the second thrust reliefpositioned on the rear side in the crankshaft rotational direction islarger than a thrust relief length at an inner end portion of the firstthrust relief positioned on the front side in the crankshaft rotationaldirection.
 2. The bearing device according to claim 1, wherein both ofthe half thrust bearings comprise the a first thrust relief on a frontside and a second thrust relief on a rear side in the crankshaftrotational direction.
 3. The bearing device according to claim 1,wherein the second thrust relief on the rear side in the crankshaftrotational direction is formed so that the thrust relief length at aninner end portion of the half thrust bearing is longer than a crushrelief length at an axial end portion of a crush relief of the halfbearing that is correspondingly arranged to the second thrust relief. 4.The bearing device according to claim 3, wherein a formula: L2≧CL×1.5 issatisfied, where the thrust relief length at the inner end portion ofthe second thrust relief on the rear side in the crankshaft rotationaldirection is L2, and the crush relief length at the axial end portion ofthe crush relief of the half bearing that is correspondingly arranged tothe second thrust relief is CL.
 5. The bearing device according to claim1, wherein the first thrust relief on the front side of the half thrustrelief in the crankshaft rotational direction is formed so that thethrust relief length at an inner end portion is shorter than a crushrelief length at an axial end portion of a crush relief of the halfbearing that is correspondingly arranged to the first thrust relief. 6.The bearing device according to claim 5, wherein a formula: L1×1.5≦CL issatisfied, where the thrust relief length at the inner end portion ofthe second thrust relief on the front side of the half thrust bearing inthe crankshaft rotational direction is L1, and a crush relief length atan axial end portion of a crush relief of the half bearing that iscorrespondingly arranged to the first thrust relief is CL.
 7. Thebearing device according to claim 1, wherein a thrust relief depth ofeach one of the first and second thrust reliefs at both circumferentialends is constant over the entire length in the radial direction of thefirst and second thrust reliefs.
 8. The bearing device according toclaim 1, wherein a thrust relief depth of each one of the first andsecond thrust reliefs at both circumferential ends is maximum at theinner end portion of the thrust relief and is made shallower toward anouter end portion of the first and second thrust reliefs.
 9. The bearingdevice according to claim 1, wherein the thrust relief length of thesecond thrust relief positioned on the rear side of each half thrustbearing in the crankshaft rotational direction is minimum at the innerend portion of the second thrust relief and is made longer toward anouter end portion, and the first thrust relief length of the thrustrelief positioned on the front side of each half thrust bearing in thecrankshaft rotational direction is constant from the inner end portionto the outer end portion of the first thrust relief.